| Volatile organic sulfur compounds (VOSCs), especially dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and methanethiol (MT) play an important role in the process of global warming, acid precipitation, and the global sulfur cycle. VOSCs concentrations in freshwater ecosystem are low due to the balance between the formation and degradation of these compounds. In freshwater ecosystem, VOSCs are formed mainly by methylation of sulfide and to a less extent from the degradation of S-containing amino acids.The majority of study concerning the use of constructed wetlands technology for Wastewater treatment is mainly focused on the regular pollutants (for example COD and BOD) removal. However, little information exists regarding to the pathways of organic matter degradation through the identification of intermediates such as volatile alkyl sulfides (VASs). Behavior studies of these compounds in Wastewater treated with constructed wetlands have become a major initiative and are very useful for understanding the degradation pathways of organic matter occurring in the constructed wetlands. In this study, a newly developed pilot-scale subsurface constructed wetlands Wastewater treatment system was sampled for one year to study the system performance with focus on the following aspects:(1). Development of analytical method for analysis of organic sulfide;(2). Performance evaluation of constructed wetlands system by statistical analysis of data obtained by long term monitoring of organic sulfur concentration under different hydraulic loading rate and different operational conditions;(3). Investigation the mechanism for the formation and degradation of organic sulfur compounds in the constructed wetlands system by monitoring the change of electronic acceptor concentrations, dissolved oxygen, and redox potential along with water depth.The major conclusions through one year study are summarized as follows: 1. A headspace solid phase microextraction (HS-SPME) followed by gas chromatography coupled to mass spectrometry (GC-MS) has been developed for the determination of trace volatile alkyl sulfides (VASs) in Wastewater from constructed wetlands. The various parameters including type of fibers, extraction time, extraction temperature, pH value, ionic strength, sample volume and desorption conditions were investigated for optimization of HS-SPME performance for dimethyl sulfide and dimethyl disulfide in the Wastewater. The experimental results showed that the linear dynamic ranges were 10-10000 and 1-10000 ng L-1 for dimethylsulfide and dimethyldisulfide, respectively. The relative standard deviations for the determination of studied compounds were less than 10%, and recoveries range from 81.03% to 94.64% and 84.01% to 100.90% for dimethylsulfide and dimethyldisufide, respectively. By using diethylsulfide as internal standard, the proposed method has been successfully applied to the determination of dimethylsulfide and dimethyldisulfide in Wastewater with satisfactory results.2. Hydraulic loading rate (HLR) and season are major factors in the performance of constructed wetlands system, while aspect ratio, water depth and granular medium size have no clear effect on the removal of contaminants in the range of operational conditions tested. The season caused significant statistical differences in the average effluent DMS and DMDS concentrations (p<0.05). The HLR caused significant statistical differences in the average effluent DMS concentration (p<0.05). Hence, HLR and season are two important factors controlling the performance of constructed wetlands system for DMS and DMDS removal.3. The sulfate, acetic acid and dissolved organic carbon concentration in the Wastewater cause important effect on the fate of DMS and DMDS in the constructed wetlands system. Results show that DMS concentrations increase with increase of removed sulfate, removed acetic acid and removed dissolved organic carbon in the constructed wetlands system.4. Results of the electronic acceptor and redox potential survey show very reducing conditions in constructed wetlands system. Coupled with the trends of sulfate concentration in the constructed wetlands system, it is highly possible that organic matter is mainly removed through sulfate reduction and methanogenesis in the present constructed wetlands system. The formation and degradation of DMS is a cycling process in the constructed wetlands system. In one hand, DMS is formed by methylation of sulfide and the degradation of S-containing amino acids under anaerobic conditions, in other hand, DMS can be degraded by sulfate reduction and methanogenesis. Results of one year study demonstrate that the present constructed wetlands system can efficiently remove volatile alkyl sulfide, indicating that degradation rate of volatile alkyl sulfide is higher than the formation rate in the constructed wetlands system.This research was supported by the National Natural Science foundation of China "Study on the degradation of organic contaminants in the constructed wetlands treating Wastewater" (No.20477033) and the National Natural Science foundation of Chongqing (No. 2004BA7019).
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